The present invention generally relates to generating square waves from sinusoidal waves, and more particularly to reducing phase noise present in a square wave generated from a sinusoidal wave.
Crystal oscillators are configured to generate an analog sinusoidal wave at a desired frequency. Due to their frequency stability, crystal oscillators are often used to provide stable clocks for digital circuits. To that end, a conventional system typically uses a buffer to convert the analog sinusoidal wave generated by the crystal oscillator into a square wave suitable for the digital circuit. Such buffers may also be used to reduce noise present in the square wave. For example, a differential amplifier may be used as a buffer between the crystal oscillator and the digital circuit, where the differential inputs reject common mode noise to reduce noise in the square wave output by the differential outputs. However, conventional buffers generally do not address or reduce phase noise present in the generated square wave. Because wireless standards such as GPS, Bluetooth, WLAN, etc., have strict phase noise requirements, there is a need to reduce the phase noise present in square waves generated from sinusoidal waves, such as those output by a crystal oscillator.